Ice-producing domes
The ancient Persians invented refrigerators without electricity over 2,400 years ago. They are called Yakhchals and are a very clever design. They preserved ice for months in the middle of the desert using mud, water, straw, sand, clay, egg whites, lime, goat hair, and ash in specific proportions.
These ancient refrigeration systems used underground chambers, up to 15m high shade walls, shallow ice-producing pools, and wind towers to maintain nighttime sub-zero temperatures amid daytime extreme heat.
This ancient dome technology is more efficient than many modern refrigerators. Some are still used today.